Tinel's Sign: (Named after French neurosurgeon Jules Tinels, 1879-1952). Tinel's sign is a tingling sensation in the distal part of an extremity in response to pressure or percussion over the site of a partially divided nerve. It can signify regeneration of the nerve.
Evaluation of the state of regeneration of peripheral nerves oftentimes involve attempts to elicit a Tinel's sign. Unfortunately, clinicians try and elicit this sign using varying degrees of force when percussing the nerve. However, any nerve will "tingle" if hit with enough force; hitting one's "funny bone" is an example. Such tingling is a positive percussion result rather than a sign of a regenerating nerve. Therefore, there can be a high incidence of false positive Tinel's signs due to high degrees of percussion force as well as a missed Tinel's sign because of too little force.
During World War I, two different physicians observed, independently of each other, that when a damaged sensory nerve is regenerating the patient experiences a tingling sensation in the area of skin supplied by that nerve. As the nerve regenerates, the sensation moves distally on the extremity, and the sign can be produced by tapping the course of the nerve on the wounded extremity. Hoffman in Germany and Jules Tinel in France both reported this phenomena in 1915, and although Hoffman actually published first, it was Tinel who received credit. In his later works, Tinel noted that the tingling sensation appeared 4-6 weeks after injury and he hypothesized that it was caused by regenerating axons.
Since that time, the inferences that can be determined from a Tinel's sign has diverged markedly from its original conception. A literature review discloses that there is really no consensus on what it actually indicates. In 1966, Phalen.sup.1 tested 654 hands with carpal tunnel syndrome and found the Tinel's sign was present in 73% of them. He concluded it was a good diagnostic sign of an entrapped nerve. However, Stewart and Eisen.sup.2 in 1978 determined that Tinel's sign had little diagnostic value. In a series of patients with carpal tunnel syndrome, 45% had a positive percussion test and, in a series of patients without carpal tunnel syndrome, 29% had a positive reading. They concluded that Tinel's sign was of little diagnostic value. Reports by Heller.sup.3 in 1986, Seror.sup.4 in 1987, and Katz.sup.5 in 1990 also concluded the Tinel sign had little diagnostic value. FNT .sup.1 Phalen, G. S. The carpal tunnel syndrome. Seventeen year's experience in diagnosis and treatment of six hundred fifty-four hands. The Journal of Bone and Joint Surgery, 48-A (2): 211-228, 1966. FNT .sup.2 Tinels sign and the carpal tunnel syndrome. British Medical Journal, 1125-1126, Oct. 21, 1978. FNT .sup.3 Heller, L., Ring, H., Costeff, H., and Solzi, P. Evaluation of Tinel's and Phalen's signs in the diagnosis of the carpal tunnel syndrome. Eur. Neuro, 25:40-42, 1986. FNT .sup.4 Seror, P. Tinel's sign in the diagnosis of carpal tunnel syndrome. The Journal of Hand Surgery, 12-B (3): 364-365, 1987. FNT .sup.5 Katz, J. N., Larson, M. G., Sabra, A. Krarup, C., Stirrat, C. R., Sethi, R., Eaton, H. M., Fossel, A. H., & Liang, M. H. The carpal tunnel syndrome: Diagnostic utility of the history and physical examination findings. Annals of Internal Medicine, 112:321-327, 1990.
More recently, applicant conducted tests to determine at what threshold force a positive percussion test is elicited for each of seven nerve locations in the forearm. With knowledge of the amount of force necessary to produce a positive test in healthy subjects, examiners could use a lesser force to ensure that the response was a true Tinel's sign and not simply the nerve responding to an excessive amount of force.
Testing was done using specially designed hammers capable of delivering a precise force of 1, 2, 3, 4, or 5 pounds. Seven locations on each forearm were tested a multiple of times at each level using each weight force on each location. If a subject felt tingling and paresthesia following an impact it was counted as a positive response. This is termed the threshold force; e.g. the lowest force which elicited the tingling sensation for each location.
The seven specific locations tested were: (1) The radial nerve in the forearm under cover of the brachioradialis muscle near the lateral epicondyle of the humerus; (2) The median nerve where it passes between the two heads of the pronator teres in the antecubital fossa; (3) The median nerve where it lies deep to the flexor carpi radialis at the wrist; (4) The ulnar nerve where it passes behind the medial epicondyle at the elbow; (5) The ulnar nerve under cover of the flexor carpi ulnaris and under the flexor retinaculum at wrist; (6) The ulnar nerve at the carpus next to the pisiform bone, and (7) The median nerve at the base of thenar eminence. These seven locations include all the nerves in the forearms which are accessible to surface touch.
Threshold readings were as follows: Site number 1, the radial nerve in the forearm near the epicondyle of the humerus--3 pounds (5.8% false positive rate); Site number 2, the median nerve in the antecubital fossa--4 pounds (4.2% false positive rate); Site number 3, the median nerve at the wrist--3 pounds (10% false positive rate); Site number 4, the ulnar nerve at the elbow--2 pounds (10.8% false positive rate); Site number 5, the ulnar nerve at the wrist--3 pounds (5% false positive rate); Site number 6, the ulnar nerve at the carpus next to the pisiform bone at the base of the palm--2 pounds (5% false positive rate); and Site number 7, the median nerve at the base of the thenar eminence--3 pounds (5% false positive rate).
The results showed the ulnar nerve at the elbow had the lowest threshold for a positive response; that is, it took less force to elicit a positive percussion test in this location than the other locations. It took only two pounds of force to elicit a tingling response in 10% of the subjects. At the other end of the spectrum, the median nerve at the antecubital fossa had the highest threshold for a positive response, that is, it took more force to elicit a positive percussion test in this location than the other locations. It took four pounds of force to elicit tingling sensation in only 4.2% of the subjects, and even at five pounds, only 6.7% had a positive response.
It was determined that each nerve has a specific threshold force which will elicit a positive percussion test. Laplace's law states that Tension=Transmural Pressure.times.Radius of the Cylinder. In other words, percussing with great force over the nerve will increase the pressure inside the nerve to the point where the nerve will depolarize and give a tingling sensation. If the nerve is percussed at this force or above, the positive reaction may be falsely interpreted as a Tinel's sign.
The differing force necessary at each location can be explained by how close to the surface the nerve is. Nerves which lie just under the skin require less force to elicit a response than those which lie under tendon and muscle. In addition, nerves which are already under pressure from disease or injury will depolarize more rapidly than a nerve not under pressure. Injured nerves, therefore, require less force to elicit a response.
With reference to the prior art, Alban, 4,505,278 discloses a plunger-type device to measure pain thresholds. It is a gradual pressure device that would not work in applicant's methods. The Torricelli patents, 2,685,286; 2,744,520 and 2,800,895, disclose spring charged reflex guns for striking reflex nerve areas. There are no standards with which the force has been calculated. The Torricelli design are apparently to act as a replacement for the ordinary reflex hammer found in most medical offices. In each device, Torricelli obtains his strength by degree of compression. Applicant, on the other hand, first determines the force necessary and then uses a force to accurately administer that force. The spring is biased the same amount for each strike.